In recent years, in accompaniment with advancement of an information system, the leakage of personal information and the spoofing of a different person in a transaction on a network have become problematic. In order to prevent these problems, an apparatus is developed that inputs features peculiar to a person and authenticates the person. Also, a smaller size and lower price of an information processing apparatus represented by a mobile phone has been advanced, and a biometrical feature inputting apparatus is also required to be miniaturized and cheapened. Moreover, the personal authentication based on the biometrical features is used for settlement of transaction by use of a credit card. For this reason, a higher precision of the biometrical feature input apparatus is required more and more, in order to surely authenticate the person under any situation.
Conventionally, this type of the biometrical feature input apparatus for personal authentication is represented by an apparatus for reading a fingerprint that is the pattern of a skin of a fingertip. The fingerprint is not same between all people and never changed in one's life. Especially, this is researched in police and justice fields and used for the personal authentication of a high precision.
For example, as described in U.S. Pat. No. 3,045,629 and U.S. Pat. No. 6,381,347, a method of using a total reflection critical angle of a fiber optic plate and a prism is widely used as a fingerprint input apparatus. The conventional fingerprint input apparatus that uses the total reflection critical angle of the prism will be described with reference to FIG. 1. The skin 104 of a finger is shown by enlarging the pattern of the skin. A lens 106 and a 2-dimensional image sensor 107 are arranged in a direction orthogonal to a prism plane 109 of a prism 105. A light beam 101 is inputted from a portion of the finger that is not in contact with the prism to a prism plane 108 having the refractive index more than 1.4 from the air layer having the refractive index of 1.0 into a prism plane 108. This is largely refracted and totally reflected on the prism plane 109, or does not arrive at the prism plane 109 and does not arrive at the 2-dimensional image sensor 107. On the other hand, the refractive index of fats and oils or water on the skin and the skin surface is close to that of a prism glass. Thus, a light beam 102 emitted from a portion of the finger with which the skin is in contact is inputted to the lens 106 without arriving at the total reflection angle on the prism plane 109, because the refractive angle of the prism plane 108 becomes small, and generates an image through the lens 106 and arrives at the two-dimensional image sensor 107. In this way, the fingerprint pattern is obtained depending on whether or not a concave/convex section pattern of the skin such as the fingerprint of the finger is brought into contact with the prism. However, this conventional fingerprint input apparatus uses an optical part that is expensive and large, which disturbed the miniaturization and lower price of the apparatus.
In order to attain the miniaturization of the fingerprint input apparatus, a technique is proposed that uses a quasi 1-dimensional sensor using a pressure, temperature and capacitance, and then links partial images of the fingerprint of the finger obtained when a finger is moved and a fingerprint image is re-assembled, and is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-91769 and JP-P2001-155137A). The technique that uses a 1-dimensional sensor and moves a read target and then reconfigures partial images is already known in a facsimile and a copier. However, this requires the special mechanism to obtain the speed in the direction in which the finger is moved. In order to omit a special mechanism, a technique proposed in Japanese Laid Open Patent Application (JP-A-Heisei 10-91769) reconfigures the partial images based on the similarity between the images on meta-1-dimensional several lines.
An image reconfiguration example of the fingerprint in this method will be described below with reference to FIGS. 2A and 2B. As an image of a finger 301, partial images I1 to In are obtained when the finger is moved. The similar partial images are removed from those partial images, and a reconfigured fingerprint image 302 is obtained. However, in this method, as shown in FIGS. 3A and 3B, when the finger is slowly moved with respect to the imaging speed of a sensor, the overlap becomes wide between the partial images adjacent to each other, and the judgment of the similarity becomes difficult. Also, an obtained fingerprint image 303 is longitudinally extended and distorted. Oppositely, if the finger is slid faster than the imaging speed, as shown in FIGS. 4A and 4B, the lost image appears between the partial images I1 to In, and longitudinally contracted and distorted such as a fingerprint image 304. In this way, this conventional example has a problem in which the fingerprint authentication, namely, the authentication based on the biometrical feature is hard to attain, if dermatitis cause the skin to be partially peeled, in addition to the foregoing problems.
Under such an environment, a non-contact fingerprint detection apparatus is proposed in, for example, Japanese Laid Open Patent Application (JP-P2003-85538A). According to this non-contact method, even in the finger that is hard to read because of difficulty in contact of the skin peeling portion in the method in which the foregoing contact is assumed, its image is obtained if a portion of the structure inside the skin resulting in a skin pattern is stored. Also, because of the non-contact, it is difficult to receive the influence of the state change on the skin surface such as a wet or dry state.
In this conventional example, a light is inputted to the finger and scattered inside the finger, and emission light is emitted from the finger to reflect the inner structure of the skin. In the thus-obtained fingerprint image, the concave section of the fingerprint becomes a bright region, and the convex section becomes a dark region, and the bright and dark image having the same shape as the fingerprint is obtained. In this way, in this conventional example, even when an epidermis horny layer is stripped and dropped due to the dermatitis, the fingerprint image is obtained independently of the wet or dry state of an epidermis if the structure of a cutis serving as a cutis pattern of the fingerprint is stored. However, in case of the fingerprint detecting apparatus described in Japanese Laid Open Patent Application (JP-P2003-85538A), unless a space is provided between the finger and an image forming system so as to accomplish the non-contact between them, an intended image cannot be obtained. Also, a frame for fixing the finger is required from the necessity of adjusting a focus, which disturbs the operability and the miniaturization of the apparatus. Also, the image forming optical system is required, which makes the apparatus larger. Also, the finger and the image forming system are separated, so that light emitted from the skin surface is scattered on the skin surface even if the inner structure of the finger causes the light quantity emitted from the skin surface to be changed. For this reason, the fingerprint image of excellent contrast cannot be obtained in the portion in which the skin is actually stripped, because of an adverse influence to the image forming system due to the separation.
For this reason, a reading apparatus that uses a physical absolute value and a change amount such as a light, an electric field, a pressure, a capacitance and a temperature, is variously developed. For example, a fingerprint input apparatus is proposed in Japanese patent No. 3150126 by the inventor of this application, in which a 2-dimensional image sensor is provided closely to the finger, and the scattered emission light from the finger is imaged through a transparent protection cover made of glass by the 2-dimensional image sensor, to obtain a fingerprint image in which the concave section of the fingerprint is a dark region and the convex section is a bright region. This conventional example is hard to receive the influence of the external environment such as the wet or dry state of the finger and the external disturbance light, as compared with the sensor that uses the pressure, the temperature, the capacitance and the total reflection critical angle, and attains the miniaturization and low price of the apparatus. However, this requires the large 2-dimensional image sensor, and although an optical system such as a lens is removed, the further miniaturization and lower price of the apparatus are obstructed. Also, as described in Japanese Laid Open Patent Application (JP-P2003-006627A) proposed by the inventor of this application, the image of high contrast can be obtained by optimally selecting the refractive index of the transparent protection cover.
Also, the fact that a fingerprint image obtained from a scattered emission light from a finger greatly depends on the boundary situation between its skin and a sensor protection film, is pointed out in Japanese Laid Open Patent Application (JP-P2003-006627A) proposed by the inventor of this application. On the other hand, the scattered emission light from the finger obviously reflects the structure inside the finger, because the light is once inputted into the finger. Thus, in the fingerprint input apparatus according to Japanese patent No. 3150126 proposed by the inventor of this application, a certain small fingerprint detecting apparatus is attained in which an optical image forming system is removed. Also, the inner structure of the skin of the finger is reflected even in the non-contact portion in which the skin is stripped, which is pointed out in Japanese Laid Open Patent Application (JP-P2003-85538A). However, when the refractive index of the transparent cover existing between the fingerprint and the 2-dimensional image sensor provided closely thereto is selected to increase the contrast between the bright region corresponding to the convex section of the fingerprint in contact with the transparent cover and the dark region corresponding to the concave that is not in contact, as described in Japanese Laid Open Patent Application (JP-P 2003-006627A), the influence of the reflection and refraction on the boundary becomes strong so that a light component reflecting the skin structure becomes small. As a result, it is difficult to obtain the contrast of the fingerprint image which reflects the skin structure originally appearing in the portion in which the skin is stripped. This problem is especially severe when a dynamic range of the image sensor cannot be widely set. When the non-contact state is kept, there is no influence on the boundary. However, it is impossible to keep the non-contact state in a constant distance from the finger having a curvature to the 2-dimensional image sensor, and it is also difficult to obtain the stable fingerprint image.
On the other hand, as the input apparatus of the biometrical feature existing on the finger, a technique for authenticating a blood vessel pattern on a finger base side below a first knuckle in addition to the fingerprint pattern is put to practical use in recent years. This technique uses the absorption of near-infrared light by blood and reads a thick blood vessel pattern such as vein. This is an application of the technique of an optical CT (Computer Tomography) earnestly researched in the 1980s, namely, the technique to perform a so-called computer tomography of a living body by using light harmless for the living body. When the near-infrared light is emitted from above the finger, the light that is passed through the finger and emitted from the cushion of the finger on the opposite side becomes dark due to the absorption of the near-infrared light by the blood in the blood vessel, and the blood vessel image is consequently obtained. For example, as disclosed in Japanese Laid Open Patent Application (JP-P2001-155137A), if this image can be read together with the fingerprint pattern, this serves as the supplement for the fingerprint information or becomes an effective information source on whether or not it is the living body, and this is effective as the judging method of a spurious finger.
However, the effective information amount of the blood vessel pattern is typically smaller than those of various fingerprints, and this is changed due to any trouble such as a nutrition state, a blood clot, and a blood pressure. As compared with the fingerprint which is mainly used in the police and justice fields because there is no same fingerprint and never changed in one's life and the research is already completed, that precision is not still checked, and remains as a future research subject. Also, similarly to the proposal (Japanese Laid Open Patent Application (JP-P2003-85538A)) of the non-contact fingerprint detection apparatus, a space is required between the fingerprint and the image forming system, and a frame for fixing the finger is required from the necessity of adjusting the focus, which obstructs the operability and the miniaturization of the apparatus. Also, only a capillary vessel exists in a fingertip, and the pattern of the capillary vessel cannot be read by the foregoing method. The readable vein blood vessel is located on the finger base side below the first knuckle. Thus, that portion must be read by a small optical system in addition to the fingerprint pattern of the fingertip above the first knuckle.
In relation to the foregoing explanation, a fingerprint detection method is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 5-168610). This fingerprint detection method of the conventional example is an optical fingerprint detecting method in which a light is emitted from a light source to a specimen including a potential fingerprint and calculates the obtained fingerprint image to detect the fingerprint. A surface temperature of the specimen is measured in advance and stored as a thermal image data, and the light of a wavelength in a region in which the absorption property is changed depending on the amount of water or organic substances included in the fingerprint component is emitted to the specimen for a certain time, and the emission light is then cut. The temperature of the specimen surface at that time is measured to obtain a thermal image data. The thermal image data prior to the light emission that is preliminarily measured and stored and the thermal image data after the light emission are converted into electronic signals, a difference in a 2-dimensional temperature distribution is calculated, and an image obtained as the calculated result is displayed, to specify the location of a fingerprint ridge section.
Also, a fingerprint information processing apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-143663). This fingerprint information processing apparatus of the conventional technique has a fingerprint image detector for detecting the fingerprint of a targeted person partially and optically. A relative position detector detects relative positions of a plurality of partial fingerprint images detected by the fingerprint image detector. An image synthesizer generates a synthesis fingerprint image by synthesizing the plurality of partial fingerprint images while compensating the mutual positional displacements between the plurality of partial fingerprint images in accordance with the relative position data detected by the relative position detector. A storage unit registers the data of the synthesis fingerprint image as a registration fingerprint image for individual identification information.
Also, a fingerprint authenticating apparatus is disclosed in Japanese Laid Open Patent Application (JP-P2002-49913A). In this fingerprint authenticating apparatus of the conventional example, a optical sensor region of an optical image sensor has an effective image region that a scattered light from inside a finger is converted into an image signal; and a black reference region that no reaction is taken for light. The black reference region may be connected with a silicon substrate that serve as a main body of the optical image sensor by a thermally conductive film, and this is formed by forming an optical light shielding film on a silicon dioxide film that covers the optical sensor region. A black reference region reader reads a dark current of a photo diode of the optical image sensor before and after the finger is placed on the optical image sensor, and a dark current comparator compares both current signals. When a difference of a predetermined value or more is detected from an image signal, a fingerprint checker acquires the image signal in the effective image region and checks and compares it with a fingerprint database. If the difference of the predetermined value or more is recognized as the comparison result of the image signal, a fingerprint determining unit determines the finger to be true, only when the feature is coincident with the fingerprint database as the result of the check.